U.S. patent application number 16/704061 was filed with the patent office on 2020-04-09 for photocathode designs and methods of generating an electron beam using a photocathode.
The applicant listed for this patent is KLA-TENCOR CORPORATION. Invention is credited to Gildardo R. Delgado, Rudy F. Garcia, Frances Hill, Katerina Ioakeimidi, Michael E. Romero.
Application Number | 20200111637 16/704061 |
Document ID | / |
Family ID | 65994019 |
Filed Date | 2020-04-09 |
United States Patent
Application |
20200111637 |
Kind Code |
A1 |
Ioakeimidi; Katerina ; et
al. |
April 9, 2020 |
PHOTOCATHODE DESIGNS AND METHODS OF GENERATING AN ELECTRON BEAM
USING A PHOTOCATHODE
Abstract
A photocathode can include a body fabricated of a wide bandgap
semiconductor material, a metal layer, and an alkali halide
photocathode emitter. The body may have a thickness of less than
100 nm and the alkali halide photocathode may have a thickness less
than 10 nm. The photocathode can be illuminated with a dual
wavelength scheme.
Inventors: |
Ioakeimidi; Katerina; (San
Francisco, CA) ; Delgado; Gildardo R.; (Livermore,
CA) ; Romero; Michael E.; (San Jose, CA) ;
Hill; Frances; (Sunnyvale, CA) ; Garcia; Rudy F.;
(Union City, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KLA-TENCOR CORPORATION |
Milpitas |
CA |
US |
|
|
Family ID: |
65994019 |
Appl. No.: |
16/704061 |
Filed: |
December 5, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16150399 |
Oct 3, 2018 |
10535493 |
|
|
16704061 |
|
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|
62570438 |
Oct 10, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 37/28 20130101;
H01J 2201/3048 20130101; H01J 2201/30411 20130101; H01J 40/18
20130101; H01J 2237/06333 20130101; H01J 1/3044 20130101; H01J
2237/24592 20130101; G02B 27/0927 20130101; H01J 37/073 20130101;
H01J 37/06 20130101; H01J 2201/3425 20130101; H01J 19/24 20130101;
H01J 37/26 20130101; H01L 21/67288 20130101; H01J 40/06 20130101;
H01J 2201/3423 20130101; H01J 1/34 20130101; H01J 2237/24521
20130101; H01J 2237/2817 20130101; H01J 2201/30449 20130101; H01J
2201/308 20130101; H01J 2201/3426 20130101 |
International
Class: |
H01J 37/073 20060101
H01J037/073; H01J 37/26 20060101 H01J037/26; G02B 27/09 20060101
G02B027/09; H01J 40/06 20060101 H01J040/06; H01J 40/18 20060101
H01J040/18; H01J 1/304 20060101 H01J001/304; H01J 19/24 20060101
H01J019/24; H01J 37/06 20060101 H01J037/06; H01J 37/28 20060101
H01J037/28 |
Claims
1. A photocathode comprising: a body fabricated of a wide bandgap
semiconductor material, wherein the body has a first surface and a
second surface opposite the first surface, and wherein the body has
a thickness between the first surface and the second surface of
less than 100 nm; a metal layer disposed on the first surface,
wherein in the metal layer is configured as an electrical contact
that applies an electric field to guide electrons toward a surface
of the photocathode; and an alkali halide photocathode emitter
disposed on the second surface, wherein the alkali halide
photocathode has a thickness less than 10 nm.
2. The photocathode of claim 1, wherein the metal layer includes
one or more of platinum or gold.
3. The photocathode of claim 1, wherein the wide bandgap
semiconductor material includes an alloy of InGaN.
4. The photocathode of claim 3, wherein the alloy of InGaN is an
alloy of InGaN and GaN.
5. The photocathode of claim 1, wherein the wide bandgap
semiconductor material includes an alloy of AlGaN.
6. The photocathode of claim 5, wherein the alloy of AlGaN is an
alloy of AlGaN and GaN.
7. The photocathode of claim 1, wherein the wide bandgap
semiconductor material includes an alloy of InGaP.
8. The photocathode of claim 7, wherein the alloy of InGaP is an
alloy of InGaP and GaP.
9. The photocathode of claim 1, wherein the wide bandgap
semiconductor material includes at least one of GaN and GaP.
10. The photocathode of claim 1, wherein the alkali halide
photocathode includes one or more of CsI, CsBr, or CsTe.
11. The photocathode of claim 1, further comprising a cap layer
disposed on the alkali halide photocathode opposite the body.
12. The photocathode of claim 11, wherein the cap layer includes
one or more of ruthenium, boron, or platinum.
13. The photocathode of claim 12, wherein the cap layer includes an
alloy of ruthenium and platinum.
14. The photocathode of claim 1, wherein the body is p-doped or
n-doped with a doping level from 10.sup.18 to 10.sup.20
cm.sup.-3.
15. An electron beam tool including the photocathode of claim 1,
wherein the electron beam tool includes a detector that receives
electrons generated by the electron emitter and reflected from a
surface of a wafer.
16. A method comprising: illuminating a photocathode with a photon
beam having a dual wavelength scheme, wherein the photocathode
includes a metal layer disposed on a first surface of a body and an
alkali halide photocathode emitter disposed on a second surface of
the body, and wherein the first surface is opposite the second
surface; applying an electric field to the metal layer thereby
guiding electrons toward a surface of the photocathode; and
generating an electron beam as the photocathode is illuminated with
the photon beam.
17. The method of claim 16, wherein the body is fabricated of a
wide bandgap semiconductor material, wherein the body has a
thickness between the first surface and the second surface of less
than 100 nm, and wherein the alkali halide photocathode has a
thickness less than 10 nm.
18. The method of claim 16, wherein both wavelengths in the dual
wavelength scheme are configured to pump.
19. The method of claim 16, wherein the dual wavelength scheme
includes a simultaneous mode with transmission and reflection.
20. The method of claim 16, wherein the dual wavelength scheme
includes a transmission mode or a reflection mode.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 16/150,399 filed on Oct. 3, 2019, which claims priority to the
provisional patent application filed Oct. 10, 2017 and assigned
U.S. App. No. 62/570,438, the disclosures of which are hereby
incorporated by reference.
FIELD OF THE DISCLOSURE
[0002] This disclosure relates to photocathodes.
BACKGROUND OF THE DISCLOSURE
[0003] Evolution of the semiconductor manufacturing industry is
placing greater demands on yield management and, in particular, on
metrology and inspection systems. Critical dimensions continue to
shrink, yet the industry needs to decrease time for achieving
high-yield, high-value production. Minimizing the total time from
detecting a yield problem to fixing it determines the
return-on-investment for a semiconductor manufacturer.
[0004] Fabricating semiconductor devices, such as logic and memory
devices, typically includes processing a semiconductor wafer using
a large number of fabrication processes to form various features
and multiple levels of the semiconductor devices. For example,
lithography is a semiconductor fabrication process that involves
transferring a pattern from a reticle to a photoresist arranged on
a semiconductor wafer. Additional examples of semiconductor
fabrication processes include, but are not limited to,
chemical-mechanical polishing (CMP), etch, deposition, and ion
implantation. Multiple semiconductor devices may be fabricated in
an arrangement on a single semiconductor wafer and then separated
into individual semiconductor devices.
[0005] Electron beams are used in a number of different
applications during semiconductor manufacturing. For example,
electron beams can be modulated and directed onto an
electron-sensitive resist on a semiconductor wafer, mask, or other
workpiece to generate an electron pattern on the workpiece.
Electron beams also can be used to inspect a wafer by, for example,
detecting electrons emerging or reflected from the wafer to detect
defects, anomalies, or undesirable objects.
[0006] These inspection processes are used at various steps during
a semiconductor manufacturing process to promote higher yield in
the manufacturing process and, thus, higher profits. Inspection has
always been an important part of fabricating semiconductor devices
such as integrated circuits (ICs). However, as the dimensions of
semiconductor devices decrease, inspection becomes even more
important to the successful manufacture of acceptable semiconductor
devices because smaller defects can cause the devices to fail. For
instance, as the dimensions of semiconductor devices decrease,
detection of defects of decreasing size has become necessary
because even relatively small defects may cause unwanted
aberrations in the semiconductor devices.
[0007] Photocathodes have been used to generate electron beams. A
single light beam incident on a photocathode system can generate a
single electron beam with high brightness that is capable of
delivering high electron current density. Single wavelengths used
to generate an electron beam were not tailored to the energy bands
of the photocathode material. Thus, the quantum efficiency (QE),
emittance, energy spread, and heat dissipation are not
optimized.
[0008] Alkali halide photocathodes such as CsI and CsBr have
demonstrated photoemission from intraband states when illuminated
with wavelengths much longer than their bandgap energy. So far, the
illumination schemes to pump these photocathodes involve either
short wavelengths with energies larger than the bandgap or longer
wavelengths that first activate the color centers located at about
4.7 eV above the valence band. These schemes have been tried both
in transmission and in reflection mode. For reflection mode, 257 nm
and 266 nm beams have successfully activated the color centers and
photogenerated electrons in vacuum. A 410 nm beam was not
successful at activating defects and simultaneously transferring
the electrons to vacuum.
[0009] Increased quantum efficiency has been demonstrated when
alkali halide materials are in contact with an
In.sub.xGa.sub.(1-x)N p-doped layer. The enhanced quantum
efficiency of this structure is because the intraband states level
aligns with the InGaN valence band (VB), which provides a pathway
of the photogenerated electrons to vacuum.
[0010] However, previous material combinations were not designed
specifically to overcome the tradeoff between quantum efficiency
and emittance that limits the source brightness. Furthermore, dual
wavelength excitation schemes or dual transmission/reflection
excitation schemes were not used for brightness optimization of the
different layers.
[0011] Therefore, improved photocathode designs and methods of
operation are needed.
BRIEF SUMMARY OF THE DISCLOSURE
[0012] A photocathode is provided in a first embodiment. The
photocathode includes a body fabricated of a wide bandgap
semiconductor material, a metal layer disposed on the first
surface, and an alkali halide photocathode emitter disposed on the
second surface. The body has a first surface and a second surface
opposite the first surface. The body has a thickness between the
first surface and the second surface of less than 100 nm. The
alkali halide photocathode has a thickness less than 10 nm.
[0013] The metal layer can include one or more of ruthenium,
iridium, platinum, or gold. For example, the metal layer can
include an alloy of ruthenium and platinum.
[0014] The wide bandgap semiconductor material can include an alloy
of InGaN. For example, the alloy of InGaN may be an alloy of InGaN
and GaN.
[0015] The wide bandgap semiconductor material can include an alloy
of AlGaN. For example, the alloy of AlGaN may be an alloy of AlGaN
and GaN.
[0016] The wide bandgap semiconductor material can include an alloy
of InGaP. For example, the alloy of InGaP may be an alloy of InGaP
and GaP.
[0017] The wide bandgap semiconductor material can include at least
one of GaN and GaP.
[0018] The alkali halide photocathode can include one or more of
CsI, CsBr, or CsTe.
[0019] The photocathode can include a cap layer disposed on the
alkali halide photocathode opposite the body. The cap layer may
include one or more of ruthenium, boron, or platinum. For example,
the cap layer can include an alloy of ruthenium and platinum.
[0020] An electron beam tool can include the photocathode of the
first embodiment. The electron beam tool can include a detector
that receives electrons generated by the electron emitter and
reflected from a surface of a wafer.
[0021] A method is provided in a second embodiment. A photocathode
is illuminated with a photon beam having a dual wavelength scheme.
The photocathode includes an alkali halide photocathode disposed on
a body. An electron beam is generated as the photocathode is
illuminated with the photon beam.
[0022] The body may be fabricated of a wide bandgap semiconductor
material. The body can have a first surface and a second surface
opposite the first surface. The body can have a thickness between
the first surface and the second surface of less than 100 nm. The
alkali halide photocathode emitter may be disposed on the second
surface. The alkali halide photocathode can have a thickness less
than 10 nm. The photocathode can further includes a metal layer
disposed on the first surface.
[0023] Both wavelengths in the dual wavelength scheme may be
configured to pump.
[0024] The dual wavelength scheme can include a simultaneous mode
with transmission and reflection.
[0025] The dual wavelength scheme can include a transmission mode
or a reflection mode.
DESCRIPTION OF THE DRAWINGS
[0026] For a fuller understanding of the nature and objects of the
disclosure, reference should be made to the following detailed
description taken in conjunction with the accompanying drawings, in
which:
[0027] FIG. 1 is a cross-sectional diagram of an embodiment of a
photocathode in accordance with the present disclosure;
[0028] FIG. 2 a photoemission model for an embodiment of the
photocathode of FIG. 1;
[0029] FIG. 3 is a bandgap structure for a CsI photocathode;
[0030] FIG. 4 is a table of pumping schemes;
[0031] FIG. 5 is a flowchart of a method embodiment in accordance
with the present disclosure; and
[0032] FIG. 6 is a block diagram of an embodiment of a system in
accordance with the present disclosure.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0033] Although claimed subject matter will be described in terms
of certain embodiments, other embodiments, including embodiments
that do not provide all of the benefits and features set forth
herein, are also within the scope of this disclosure. Various
structural, logical, process step, and electronic changes may be
made without departing from the scope of the disclosure.
Accordingly, the scope of the disclosure is defined only by
reference to the appended claims.
[0034] Embodiments of a photocathode that includes a metallic
contact (electrical contact), wide bandgap semiconductor (WBS),
alkali halide (AH), and an optional cap layer are disclosed.
Embodiments of this multilayer structure can affect the alignment
of the intraband states with the valence band of the wide bandgap
semiconductor to maximize the pathway opportunities for the
photogenerated electrons to escape to vacuum while protecting the
wide bandgap semiconductor surface. Embodiments disclosed herein
provide emittance improvement over negative electron affinity (NEA)
wide bandgap photocathodes.
[0035] FIG. 1 is a cross-sectional diagram of an embodiment of a
photocathode 100. The photocathode 100, which may be planar,
includes a body 101 with a first surface 105 and an opposite second
surface 106. In an instance, the body has a thickness 107 between
the first surface 105 and second surface 106 of less than 100 nm. A
thickness 107 of 100 nm or more may provide inferior
performance.
[0036] The body 101 can be made of a wide bandgap semiconductor
material. In an embodiment, the wide bandgap semiconductor material
includes an alloy of InGaN, such as an alloy of InGaN and GaN. In
another embodiment, the wide bandgap semiconductor material
includes an alloy of AlGaN, such as an alloy of AlGaN and GaN. In
yet another embodiment, the wide bandgap semiconductor material
includes an alloy of InGaP, such as an alloy of InGaP and GaP. In
yet another embodiment, the wide bandgap semiconductor material
includes at least one of GaN and GaP. Alloys of InGaN and GaN,
AlGaN and GaN, and InGaP and GaP may be multi-quantum well
structures. Such multi-quantum well structures can alternate layers
of two materials deposited using molecular beam epitaxy or other
techniques. Use of the wide bandgap semiconductor material can
provide greater stability. For example, initial testing with GaN
and AlGaN has provided improved results compared to previous
designs.
[0037] The body 101 can include various p-doping or n-doping
profiles or levels. The doping levels may be from 10.sup.18 to
10.sup.20 cm.sup.-3.
[0038] The material or materials of the body 101 can optimize the
alignment of the alkali halide intraband energy states with the
alloy's valence band.
[0039] A metal layer 103 is disposed on the first surface 105, and
can serve as an electrical contact. Thus, the metal layer 103 can
enable application of an electric field to guide the electrons
toward a surface of the photocathode 100. The metal layer 103 can
include one or more of ruthenium, iridium, platinum, or gold. For
example, the metal layer 103 can include an alloy of ruthenium and
platinum. The metal layer 103 can have uniformity, continuity, and
roughness configured to provide improved performance.
[0040] An alkali halide photocathode emitter 102 is disposed on the
second surface 106. The alkali halide photocathode emitter 102 can
have a non-zero thickness less than 20 nm, such as a non-zero
thickness of less than 10 nm. This thickness of the alkali halide
photocathode emitter 102 is between the second surface 106 of the
body 101 and the cap layer 104 in FIG. 1. In an instance, the
thickness of the alkali halide photocathode emitter 102 is from 1
nm to 7 nm, including all values to the 0.1 nm and ranges in
between. Thicknesses greater than 20 nm may inhibit electron
escape. The alkali halide photocathode 102 can include one or more
of CsI, CsBr, or CsTe.
[0041] A cap layer 104 may optionally be disposed on the alkali
halide photocathode 102 opposite the body 101. The cap layer 104
can include one or more of ruthenium, boron, or platinum. For
example, the cap layer 104 can include an alloy of ruthenium and
platinum. The cap layer 104 can have uniformity, continuity, and
roughness configured to provide improved performance.
[0042] The cap layer 104 can provide protection to the photocathode
100 and can enable photocathode 100 operation in higher vacuum
conditions. The cap layer 104 may reduce oxidation or carbon
contamination of the photocathode 100. The cap layer 104 also may
enable plasma cleaning of the photocathode 100.
[0043] Ruthenium may have the ability to break apart gas molecules
that land on its surface or prevent adherence of such gas molecules
to its surface. These molecules are capable of distorting the
extraction field on the surface of the photocathode 100 and causing
enhanced emission which translates as noise in the electron beam
because of the mobility and residence time of the molecule on the
surface. Thus, a cap layer 104 with ruthenium can be
self-cleaning.
[0044] Thickness of the layers in the photocathode 100 can be
configured to optimize electron emission or to provide maximum
quantum efficiency. The exact thickness of the layers may depend on
the photocathode 100 extractor configuration and wavelength used
for photo electron emission.
[0045] FIG. 2 a photoemission model for an embodiment of the
photocathode 100 using GaN and CsBr. Similar photoemission models
exist for other materials that can be used in the photocathode 100.
As seen in FIG. 2, the multilayer structure affects alignment of
the intraband states with the valence band of the wide bandgap
semiconductor in the body 101 to maximize pathway opportunities for
the photogenerated electrons to escape to vacuum while protecting
the surface of the body 101.
[0046] A wide bandgap semiconductor that has a high photo yield
such as GaN may not require negative electron affinity conditions
and can operate at lower vacuum conditions and have longer
lifetime.
[0047] Quantum efficiency of the alkali halide photocathodes based
on intraband states can be improved due to the photogenerated
electrons in the wide bandgap semiconductor region even when
illuminated with wavelengths longer than the bandgap energy. The
high quantum efficiency of the disclosed photocathode tailors the
emittance characteristics of the source to the energy and angular
spread of the alkali halide photocathodes, which can provide a high
brightness source.
[0048] Single or dual wavelength pumping schemes in transmission,
reflection, or transmission and reflection simultaneous mode can be
used to optimize brightness. The transmission and reflection light
can be different wavelengths. The mode of operation (transmission,
reflection, or both), and wavelengths used can be used to determine
optical thickness of the metal layer 103, the body 101, the alkali
halide photocathode emitter 102, and/or the cap layer 104.
[0049] In an instance, using optimized wide bandgap semiconductor
alloys in combination with an alkali halide layer can provide high
brightness photocathode structures pumped with dual wavelength
schemes and/or in concurrent reflection and transmission pumping
modes.
[0050] The brightness of the photocathode emitters may depend on
the photocathode material and the excitation wavelength with a
general tradeoff between quantum efficiency and emittance.
[0051] Embodiments of the photocathode 100 can be used as the
electron source in reticle and wafer inspection systems. For
example, embodiments of the photocathode 100 can be used as the
electron source in electron beam wafer or reticle inspection
systems using single or multiple electron sources, electron beam
wafer or reticle review systems using single or multiple electron
sources, or electron beam wafer or reticle metrology systems using
single or multiple electron sources. Embodiments of the
photocathode 100 also can be used in systems that require electron
sources for generation of x-rays using single or multiple electron
sources for use of wafer or reticle metrology, review, or
inspection.
[0052] Multiple wavelengths can be applied to the photocathode
structure 101 that includes an alkali halide, such as CsBr, CsI, or
CsTe. The multiple wavelengths can be applied in both reflection
and transmission mode to activate and pump intraband states (e.g.,
color centers) of the alkali halide. The multiple wavelengths can
activate the centers, transfer electrons to vacuum, and overcome
defects.
[0053] Use of multiple wavelengths can increase quantum efficiency
and/or achieve the same quantum efficiency as with a single
wavelength while producing less heat. Less complex lasers systems
can be used to generate multiple wavelengths than a single
wavelength. For example, a longer wavelength can use a less complex
laser system or optics. Less energy spread of the photogenerated
electrons and lower emittance can be achieved.
[0054] Based on the wavelength assignment of FIG. 3, the proposed
pumping schemes are: activate color centers with .lamda.1 and pump
the cathode with .lamda.2; activate with .lamda.1, pump with
.lamda.1 and .lamda.2; and/or pump with .lamda.1 and .lamda.3. FIG.
3 illustrates the conduction band (CB) and valence band (VB).
[0055] The third pumping scheme using two wavelengths may be an
equivalent to electromagnetically-induced transparency (EIT) where
.lamda.1 blocks the color centers from absorbing .lamda.3, which
can enable electrons to be pumped directly from the valence band to
vacuum. A potential combination of wavelengths for CsI is shown in
the table of FIG. 4.
[0056] The dual wavelength pumping scheme can minimize required
optical power per photogenerated electron, which can provide higher
quantum efficiency. Heat dissipation per photogenerated electron
also can be minimized. A dual wavelength pumping scheme also can
provide improved localization of induced current.
[0057] Dual wavelength pumping schemes can be performed
concurrently in transmission and reflection mode, which can
optimize efficiency.
[0058] Longer photocathode and optics lifetimes can be achieved
with longer wavelength illumination, such as those using a dual
wavelength pumping scheme.
[0059] Lower emittance and energy spread can be achieved using
longer wavelengths, such as with a dual wavelength pumping scheme.
Wavelengths can be tailored to provide a desired energy transition
to satisfy the tradeoff between quantum efficiency and transverse
energy spread.
[0060] FIG. 5 is a flowchart of a method 200. A photon beam
illuminates a photocathode with a dual wavelength scheme at 201.
The photocathode includes an alkali halide photocathode.
[0061] An electron beam is generated as the photocathode is
illuminated with the photon beam at 202. The dual wavelength scheme
can operate at short wavelengths, which can include deep
ultraviolet wavelengths. This can provide low noise, high
stability, and low energy spread. The photocathode may be the
photocathode 100, for example.
[0062] In an instance, the photocathode includes an alkali halide
layer disposed on a body, such as that illustrated in FIG. 1. The
body may be fabricated of a wide bandgap semiconductor material and
can have a first surface and a second surface opposite the first
surface. The body may have a thickness between the first surface
and the second surface of less than 100 nm. The alkali halide
photocathode emitter can be disposed on the second surface and can
have a thickness less than 10 nm. The photocathode also can include
a metal layer disposed on the first surface. Other photocathode
configurations with an alkali halide layer are possible.
[0063] Both wavelengths in the dual wavelength scheme may be
configured to pump. The dual wavelength scheme also can include a
simultaneous mode with transmission and reflection, with
transmission, or with reflection.
[0064] FIG. 6 is a block diagram of an embodiment of a system 300.
The system 300 includes a wafer inspection tool (which includes the
electron column 301) configured to generate images of a wafer
304.
[0065] The wafer inspection tool includes an output acquisition
subsystem that includes at least an energy source and a detector.
The output acquisition subsystem may be an electron beam-based
output acquisition subsystem. For example, in one embodiment, the
energy directed to the wafer 304 includes electrons, and the energy
detected from the wafer 304 includes electrons. In this manner, the
energy source may be an electron beam source. In one such
embodiment shown in FIG. 6, the output acquisition subsystem
includes electron column 301, which is coupled to computer
subsystem 302. A chuck (not illustrated) may hold the wafer
304.
[0066] As also shown in FIG. 6, the electron column 301 includes an
electron beam source 303 configured to generate electrons that are
focused to wafer 304 by one or more elements 305.
[0067] The electron beam source 303 may include, for example, an
embodiment of the photocathode 100 of FIG. 1. The one or more
elements 305 may include, for example, a gun lens, an anode, a beam
limiting aperture, a gate valve, a beam current selection aperture,
an objective lens, and a scanning subsystem, all of which may
include any such suitable elements known in the art. The
photocathode 100 can operate using the method 200 or other
embodiments disclosed herein.
[0068] Electrons returned from the wafer 304 (e.g., secondary
electrons) may be focused by one or more elements 306 to detector
307. One or more elements 306 may include, for example, a scanning
subsystem, which may be the same scanning subsystem included in
element(s) 305.
[0069] The electron column also may include any other suitable
elements known in the art.
[0070] Although the electron column 301 is shown in FIG. 6 as being
configured such that the electrons are directed to the wafer 304 at
an oblique angle of incidence and are scattered from the wafer 304
at another oblique angle, the electron beam may be directed to and
scattered from the wafer 304 at any suitable angles. In addition,
the electron beam-based output acquisition subsystem may be
configured to use multiple modes to generate images of the wafer
304 (e.g., with different illumination angles, collection angles,
etc.). The multiple modes of the electron beam-based output
acquisition subsystem may be different in any image generation
parameters of the output acquisition subsystem.
[0071] Computer subsystem 302 may be coupled to detector 307 such
that the computer subsystem 302 is in electronic communication with
the detector 307 or other components of the wafer inspection tool.
The detector 307 may detect electrons returned from the surface of
the wafer 304 thereby forming electron beam images of the wafer 304
with the computer subsystem 302. The electron beam images may
include any suitable electron beam images. The computer subsystem
302 includes a processor 308 and an electronic data storage unit
309. The processor 308 may include a microprocessor, a
microcontroller, or other devices.
[0072] It is noted that FIG. 6 is provided herein to generally
illustrate a configuration of an electron beam-based output
acquisition subsystem that may be used in the embodiments described
herein. The electron beam-based output acquisition subsystem
configuration described herein may be altered to optimize the
performance of the output acquisition subsystem as is normally
performed when designing a commercial output acquisition system. In
addition, the systems described herein may be implemented using an
existing system (e.g., by adding functionality described herein to
an existing system). For some such systems, the methods described
herein may be provided as optional functionality of the system
(e.g., in addition to other functionality of the system).
Alternatively, the system described herein may be designed as a
completely new system.
[0073] The computer subsystem 302 may be coupled to the components
of the system 300 in any suitable manner (e.g., via one or more
transmission media, which may include wired and/or wireless
transmission media) such that the processor 308 can receive output.
The processor 308 may be configured to perform a number of
functions using the output. The wafer inspection tool can receive
instructions or other information from the processor 308. The
processor 308 and/or the electronic data storage unit 309
optionally may be in electronic communication with another wafer
inspection tool, a wafer metrology tool, or a wafer review tool
(not illustrated) to receive additional information or send
instructions.
[0074] The computer subsystem 302, other system(s), or other
subsystem(s) described herein may be part of various systems,
including a personal computer system, image computer, mainframe
computer system, workstation, network appliance, interne appliance,
or other device. The subsystem(s) or system(s) may also include any
suitable processor known in the art, such as a parallel processor.
In addition, the subsystem(s) or system(s) may include a platform
with high speed processing and software, either as a standalone or
a networked tool.
[0075] The processor 308 and electronic data storage unit 309 may
be disposed in or otherwise part of the system 300 or another
device. In an example, the processor 308 and electronic data
storage unit 309 may be part of a standalone control unit or in a
centralized quality control unit. Multiple processors 308 or
electronic data storage unit 309 may be used.
[0076] The processor 308 may be implemented in practice by any
combination of hardware, software, and firmware. Also, its
functions as described herein may be performed by one unit, or
divided up among different components, each of which may be
implemented in turn by any combination of hardware, software and
firmware. Program code or instructions for the processor 308 to
implement various methods and functions may be stored in readable
storage media, such as a memory in the electronic data storage unit
309 or other memory.
[0077] The system 300 of FIG. 6 is merely one example of a system
that can use the electron source 100. Embodiments of the electron
source 100 may be part of a defect review system, an inspection
system, a metrology system, or some other type of system. Thus, the
embodiments disclosed herein describe some configurations that can
be tailored in a number of manners for systems having different
capabilities that are more or less suitable for different
applications.
[0078] Each of the steps of the method may be performed as
described herein. The methods also may include any other step(s)
that can be performed by the processor and/or computer subsystem(s)
or system(s) described herein. The steps can be performed by one or
more computer systems, which may be configured according to any of
the embodiments described herein. In addition, the methods
described above may be performed by any of the system embodiments
described herein.
[0079] Although the present disclosure has been described with
respect to one or more particular embodiments, it will be
understood that other embodiments of the present disclosure may be
made without departing from the scope of the present disclosure.
Hence, the present disclosure is deemed limited only by the
appended claims and the reasonable interpretation thereof.
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